Modem communication systems increasingly rely upon fiber optic networks to carry increasing amounts of data between networks and systems. For example, the use of multiple optical carriers (called channels) over a same optical fiber can increase signal bandwidth and capacity. Such communication systems include analog optical communication systems. The utilization of analog optical communication systems for analog applications previously associated with traditional technologies such as standard wire-based communication systems, and telephony and cable television (CATV) is driven in part by the increasing availability of broadband optical fiber networks in businesses and homes.
An analog optical communication system transmits an analog information signal over an optical fiber by modulating a carrier light beam with an information signal, and transmitting the modulated carrier over the optical fiber to an optical receiver. For long-distance applications, high optical power levels are needed to avoid the needs for compensational network components such as amplifiers and repeaters, which can substantially increase the overall cost and complexity for deploying the system.
However, the use of high optical power level (e.g., using a high-powered, narrow-linewidth optical source) in combination with the use of conventional optical fiber can lead to various non-linear effects that can cause signal degradation. Non-linear effects generally arise through interactions between optical carriers of relatively high power and the transmission medium through which the optical carriers are transmitted (e.g., optical fibers and other waveguides). One such non-linear effect includes four-wave mixing (FWM). FWM generally occurs between close, neighboring channels, and in optical fibers having low dispersion within the desired band (e.g., within the range of signal wavelengths).
Although FWM occurs generally in optical communication systems, FWM is most prevalent in high speed systems such as wavelength division multiplexing (WDM) systems and coarse WDM (CWDM) systems. FWM can place significant limitations on the deployment of these systems, and can degrade the desired signals being transmitted.